The induction of myocardial damage by open-chest low-energy countershock.

Anesthetized rabbits were used to study the effects of internal electrical defibrillation on the heart. Single electrical shocks of 0.5, 1.0, and 3.0 Wsec/kg or five consecutive shocks of 0.5 Wsec/kg spaced at either 1 shock per min, per 2 min, or per 3 min, were used. Half of the rabbits given a single shock of 1 Wsec/kg or multiple shocks at a spacing of 1 shock per min were given intravenous injection of dexamethasone sodium phosphate (6 mg/kg) 5 min before receiving the defibrillatory shocks. Damage to the hearts was assessed by electrocardiography and histopathology. Myocardial damage was evident at the lowest energy levels used. All indices showed that the degree of damage was increased by increasing the energy level of single shocks or by decreasing the time interval between multiple shocks. The steroid pretreatment did not appear to protect the hearts from damage caused by the shocks.